This invention relates to techniques for improving the effectiveness of medical electrodes and more particularly relates to techniques for improving uniformity of current flow throughout the surface area of medical electrodes and for reducing skin damage in use of such medical electrodes.
Medical electrodes constructed for monitoring of electrical activity within a patient's body typically have a relatively small surface area and are connected to electronic circuitry through an attachment mechanism that may be located at the center of the electrode.
Electrodes constructed for defibrillation or cardioversion typically have a much larger surface area and are connected to a power source through an attachment mechanism that is typically located near an edge of the electrode. Certain defibrillation or cardioversion electrodes, however, are connected to the power source through an attachment mechanism located at the center portion (the center and near-center locations) of the electrode.
For example, an R2 Medical Systems liquid gel, multi-purpose (defibrillation and sensing), disk-shaped electrode is attached to a power source through a wire that is soldered to a rectangular tab that in turn contacts the back of the electrode over a region extending from the periphery of the electrode to the center of the electrode. The point at which the wire is soldered to the rectangular tab is above the center of the electrode. The presence of the rectangular tab detracts from circular uniformity of the electrode/attachment mechanism combination.
Way, U.S. Pat. No. 5,356,428, and Ilvento et al., U.S. Pat. No. 5,366,497 disclose a disk-shaped electrode in the form of a disk-shaped mesh that is soldered to a wire near the center of the mesh. The mesh structure of the electrode detracts from circular uniformity of the electrode/attachment mechanism combination.
Input electrical current typically tends to be concentrated at the peripheries of electrodes, where the resultant reddening or skin damage is usually most noticeable. The Zoll STAT PADZ multi-purpose electrode assembly currently in use, and an electrode described in U.S. Pat. No. 5,330,526 is somewhat effective at providing reduced reddening of skin or skin damage caused by defibrillation, because the total length of the periphery of the electrode is high due to its scalloped or daisy shape.
Ferrari, U.S. Pat. Nos. 5,571,165 and 5,733,324 disclose a defibrillation electrode that is attached to a power source through a multi-strand wire in which the strands are spread out and bonded to a center portion of a rectangular current distributing mat that contacts a center portion of a rectangular electrode. The other side of the electrode contacts one or more silver/silver chloride coatings that are more conductive than the electrode and that have serrated or undulated outer perimeters spaced inwardly from the perimeter of the electrode. The patent states that the silver/silver chloride coatings improve the uniformity of current distribution between the electrode and the skin surface of the patient by reducing current density at the perimeter of the electrode and by increasing the effective perimeter of the electrode. The electrode assembly reduces reddening or skin damage because of the serrated or undulated outer perimeters, and because the central region of the assembly has higher conductivity than more peripheral regions.
Of course, there is a limit to how much of an increase in periphery or how many added layers or thicknesses of such may be practically realized. Increasing the length of the periphery of an electrode by continued surface convolutions eventually leads to convolutions so small or so close to one another that their effect is substantially negated. Increasing the thickness of an electrically conductive layer or adding additional electrically conductive layers could eventually lead to a conductive surface too rigid to accommodate patient contours, which could result in localized differences in the effective distance between the electrode and the patient, thereby resulting in localized power concentrations and reddening.